“Six to twelve months prior to the Final Oral Exam, students must give an informal public pre-defense seminar” – Meteorology Graduate Student Handbook

What is a pre-defense?

“Six to twelve months prior to the Final Oral Exam, students must give an informal public pre-defense seminar” – Meteorology Graduate Student Handbook

“Both the thesis adviser and the student are responsible for ensuring the completion of a draft of the thesis and for adequate consultation with members of the thesis committee well in advance of the oral examination” – Graduate Program Degree Bulletin

Two views:

For public to raise any concerns prior to final oral exam

For committee to get up to speed prior to defense

A third view:

What is a pre-defense?

For the student

A retrospective and a chance to show that you’ve done the hard work and it’s not as bad as it looks

Motivation

Motivation

2. The effects of disturbance and land management on surface-atmosphere exchange are poorly understood

Motivation

2. The effects of disturbance and land management on surface-atmosphere exchange is poorly understood

Motivation

3. The upper-Midwest USA is a complex, managed, heavily forested & densely-instrumented landscape that is ideal for testing the roles of disturbance, management and scaling on the regional carbon cycle

Questions & Hypotheses

What is the role of disturbance and land management on surface-atmosphere exchange on carbon dioxide?

To what extent can regional carbon balance be scaled using only dominant ecosystem types and coarse-resolution ecosystem models parameterized with global biome-scale parameters?

Do multiple top-down and bottom-up scaling methods with a high density observation network converge to the regional carbon flux?

Approach

Theory

Turbulent stand-scale measurements of vertical velocity and CO2, when properly screened for nocturnal drainage and representative surface-layer footprints, can be used to derive stand-scale carbon exchange parameters

Stand age since disturbance and carbon balance

Ecological theories on carbon dynamics with plant succession can be confirmed with observations and parameterized in models

Top-down and bottom-up scaling

Regional carbon balance can be assessed with linear scaling of observed fluxes using land cover inventories

Atmospheric mass-balance approaches can be used with sufficient inflow and outflow data coverage

Impact of Stand Age

Unmanaged site had greater temperature – respiration sensitivity

Unmanaged site had similar low radiation – photosynthesis sensitivity to mature site, but lower maximum capacity

Confirms standard theories of net carbon production and stand age

Impact of Stand Age

Both sites had significant nonhomogenous respiration responses with wind direction

Venting anomaly diagnosed for mature hardwood site

Influence of landcover found at unmanaged site, and small effect of nocturnal slope drainage (horizontal advection)

Horst and Weill surface layer footprint model used to diagnose impact of landcover combined with method of Martano (2000) to use sonic anemometer data to get surface roughness and displacement as functions of wind direction

Net carbon fluxes computed by aggregation method

Aggregation net fluxes show larger uptake than tall tower, but close agreement when tall tower fluxes are decomposed and re-extended

Biome-scale biogeochemical models make each “cell” as a single plant functional type (or fractions of a few) with grid average values of biomass and fluxes

Age can only be modeled by following a cell with time as it builds up and loses biomass

Gap models simulate the growth and fate of every plant with explicit interaction among them

Computationally expensive, difficult to parameterize

The Ecosystem Demography model (ED) (Moorcroft et al., 2001) is a size-and-age structured gap model that uses concepts of statistical mechanics and Reynolds averaging to simulate the dynamics of the mean-moment ensemble of gaps